Xylanases (e.g., endo-1,4-beta-xylanase, EC 3.2.1.8) hydrolyze internal β-1,4-xylosidic linkages in xylan to produce smaller molecular weight xylose and xylo-oligomers. Xylans are polysaccharides formed from 1,4-β-glycoside-linked D-xylopyranoses. Xylanases are of considerable commercial value, being used in the food industry, for baking and fruit and vegetable processing, breakdown of agricultural waste, in the manufacture of animal feed and in pulp and paper production. Xylanases are formed by fungi and bacteria.
Arabinoxylans are major non-starch polysaccharides of cereals representing 2.5-7.1% w/w depending on variety and growth conditions. The physicochemical properties of this polysaccharide are such that it gives rise to viscous solutions or even gels under oxidative conditions. In addition, arabinoxylans have high water-binding capacity and may have a role in protein foam stability. All of these characteristics present problems for several industries including brewing, baking, animal nutrition and paper manufacturing. In brewing applications, the presence of xylan results in wort filterability and haze formation issues. In baking applications (especially for cookies and crackers), these arabinoxylans create sticky doughs that are difficult to machine and reduce biscuit size. In addition, this carbohydrate is implicated in rapid rehydration of the baked product resulting in loss of crispiness and reduced shelf-life. For monogastric animal feed applications with cereal diets, arabinoxylan is a major contributing factor to viscosity of gut contents and thereby adversely affects the digestibility of the feed and animal growth rate. For ruminant animals, these polysaccharides represent substantial components of fiber intake and more complete digestion of arabinoxylans would facilitate higher feed conversion efficiencies.
Xylanases have been shown to be useful in biobleaching and treatment of chemical pulps (see, for example, U.S. Pat. No. 5,202,249), biobleaching and treatment of wood or paper pulps (see, for example, U.S. Pat. Nos. 5,179,021, 5,116,746, 5,407,827, 5,405,769, 5,395,765, 5,369,024, 5,457,045, 5,434,071, 5,498,534, 5,591,304, 5,645,686, 5,725,732, 5,759,840, 5,834,301, 5,871,730 and 6,057,438) in reducing lignin in wood and modifying wood (see, for example, U.S. Pat. Nos. 5,486,468 and 5,770,012) as flour, dough and bread improvers (see, for example, U.S. Pat. Nos. 5,108,765 and 5,306,633) as feed additives and/or supplements, as set forth above (see, for example, U.S. Pat. Nos. 5,432,074, 5,429,828, 5,612,055, 5,720,971, 5,981,233, 5,948,667, 6,099,844, 6,132,727 and 6,132,716), in manufacturing cellulose solutions (see, for example, U.S. Pat. No. 5,760,211). Detergent compositions having xylanase activity are used for fruit, vegetables and/or mud and clay compounds (see, for example, U.S. Pat. No. 5,786,316). Xylanases may also be used in hydrolysis of hemicellulose for which it is selective, particularly in the presence of cellulose. Additionally, the cellulase rich retentate is suitable for the hydrolysis of cellulose (see, for example, U.S. Pat. No. 4,725,544).
There remains a need in the art for xylanases to be used in the paper and pulp industry, for example, where the enzyme is active in the temperature range of 65° C. to 75° C. and at a pH of approximately 10. Additionally, an enzyme useful in the paper and pulp industry would decrease the need for bleaching chemicals, such as chlorine dioxide.